1. Field of the Invention
The present invention relates to a liquid crystal dispensing system and a method for manufacturing a liquid crystal display device using the same, and particularly, to a liquid crystal dispensing system capable of preventing or minimizing a fabrication of a defective liquid crystal panel caused by an external impact.
2. Discussion of the Related Art
As various portable electric devices such as mobile phones, personal digital assistants (PDA), notebook computers, etc., continue to be developed, various types of flat panel display devices such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum florescent displays (VFDs), which have such advantages as compact construction, light weight and low power-consumption, also continue to be developed. Owing to their simple driving scheme and superior ability to display images, LCDs are widely used in many electric devices.
An LCD device is a device that displays information on a screen by using the refractive anisotropy characteristics of liquid crystal. FIG. 1 is a cross-sectional view illustrating an LCD device according to the related art.
Referring to FIG. 1, the LCD device 1 includes a lower substrate 5, a upper substrate 3 and a liquid crystal layer 7 formed therebetween. The lower substrate 5 (i.e., a driving device array substrate) includes a plurality of pixels (not shown), with a driving device (e.g., a thin film transistor (TFT)) and a pixel electrode formed at each pixel. The upper substrate 3 (i.e., a color filter substrate) includes a color filter layer for reproducing color images and a common electrode. Alignment layers are formed on both the lower and upper substrates 5 and 3 to align the liquid crystal molecules of the liquid crystal layer 7.
The lower substrate 5 and the upper substrate 3 are attached to each other by a sealant material 9 formed at peripheral regions thereof, and the liquid crystal layer 7 is confined within an area defined by the seal material 9. The light transmittance characteristics of the pixels are controlled by electric fields between the pixel electrodes and the common electrode. The electric fields reorient the liquid crystal molecules of the liquid crystal layer 7 to display a picture.
FIG. 2 is a flow chart illustrating a method for fabricating the related art LCD device illustrated in FIG. 1.
Referring to FIG. 2, a method for fabricating the related art LCD device includes three sub-processes: a TFT array substrate forming process; a color filter substrate forming process; and a cell forming process.
In step S101, A plurality of gate lines and data lines are formed on the lower substrate 5 (e.g., a glass substrate) to define an array of pixel areas according to the TFT array substrate forming process. TFTs are connected to the gate lines and the data lines within each pixel area, and pixel electrodes are connected to the thin film transistors to drive a subsequently provided liquid crystal layer in accordance with signals applied through the thin film transistors.
In step S104, R, G and B color filter layers for displaying color images and a common electrode are formed on the upper substrate 3 (i.e., a glass substrate) according to the color filter process.
In steps of S102 and S105, alignment layers are formed on the surfaces of both the lower substrate 5 and upper substrate 3. Subsequently, the alignment layers are rubbed to induce surface anchoring (i.e., a pretilt angle and alignment direction) within the liquid crystal molecules of the liquid crystal layer 7.
In step S103, spacers are dispersed onto the lower substrate 5. In step S106, a sealant material is printed at peripheral regions of the upper substrate 3. In step S107, the lower and upper substrates 5 and 3 are pressed and bonded together (i.e., assembled) and the spacers dispersed at step S103 maintain a uniform cell gap between the assembled lower and upper substrates 5 and 3.
In step S108, the assembled upper and lower substrates 5 and 3, which are large glass substrates, are cut into unit panels. Specifically, each of the lower substrate 5 and the upper substrate 3 includes a plurality of unit panel areas and each unit panel includes individual TFT arrays and color filters.
In step S109, a liquid crystal material is injected into the cell gap of each of the unit panels through a liquid crystal injection hole defined within the sealant material. After each cell gap is completely filled with the liquid crystal material, the liquid crystal injection hole is sealed. In step S110, the filled and sealed unit panels are then tested. Here, the liquid crystal material is injected through the injection hole because of a pressure difference.
FIG. 3 illustrates a liquid crystal injection system according to the related art for fabricating an LCD device.
Referring to FIG. 3, a container 12 containing a liquid crystal material 14 is placed into a vacuum chamber 10 connected to a vacuum pump (not shown). Subsequently, a unit panel 1 formed as described above with respect to FIG. 2 is arranged over the container 12 using a unit panel handling device (not shown). Next, the vacuum pump is operated to reduce the pressure within the vacuum chamber 10 to a predetermined vacuum state. The unit panel handling device then lowers the unit panel 1 such that a liquid crystal injection hole 16 contacts a surface of the liquid crystal material 14. After the contact is established, the liquid crystal material 14 contained within the container 12 can be intaken to the cell gap of the unit panel 1 through the liquid crystal injection hole 16. The injection method described above is known as a dipping injection method.
After the contact is established, the rate at which the liquid crystal material 14 is intaken to the cell gap of the unit panel 1 can be increased by pumping nitrogen gas (N2) into the vacuum chamber 10, thereby increasing the pressure within the vacuum chamber 10. As the pressure within the vacuum chamber 10 increases, a pressure difference between the cell gap of the unit panel 1 and the interior of the vacuum chamber 10 is created. Accordingly, the liquid crystal material 14 contained in the container 12 can be injected into the cell gap of the unit panel 1 at an increased injection rate. As mentioned above, once the cell gap of the unit panel 1 is completely filled with the liquid crystal material 14, the injection hole 16 is sealed by a sealant and the injected liquid crystal material 14 is sealed within the unit panel 1. The injection method described above is known as a vacuum injection method.
Despite their usefulness, there are several problems with the aforementioned dipping and vacuum injection methods.
First, it takes a relatively long time for the dipping/vacuum injection methods to completely fill the cell gap of the unit panel 1 with the liquid crystal material 14. Specifically, because the cell gap of the unit panel 1 is only a few micrometers wide, only a small amount of the liquid crystal material 14 can be injected into the unit panel 1 per unit time. For example, it can takes about 8 hours to completely inject the liquid crystal material 14 into the cell gap of a 15-inch liquid crystal display panel, which decreases the production efficiency.
Second, the aforementioned dipping/vacuum injection methods require an excessively large amount of the liquid crystal material 14. Only a small amount of the liquid crystal material 14 is actually injected into the unit panel 1. Because the liquid crystal material 14 contained in the container 12 is exposed to the atmosphere or certain other process gases during loading and unloading of the unit panel 1 in and out of the vacuum chamber 10, the liquid crystal material 14 can easily become contaminated. Therefore, the remaining liquid crystal material 14 should be discarded, which increases the production cost.